TRIBE I. ASTR^EACEA. 321 



differ from the Agaricise in not having the intervals between trans- 

 verse series of polyps raised into ridges or folds, nor excavate cells 

 like some of the subgerius Mycedia. The Psammocorse sometimes 

 resemble the Pavonise, but are distinct, in the lamellae not being so 

 regular and so nearly entire, and the stars much less neat, or even 

 indistinct. 



The species of this genus are confined to the warm coral-reef seas, 

 and mostly to the Indian and Pacific Oceans. 



The genus Pavonia was instituted by Lamarck for the bifacial foli- 

 aceous species here included, together with the Tridacophyllise, of 

 which Blainville made a distinct genus. Some unifacial species, 

 having the essential characters of the genus, are here restored to it, 

 which have been placed with the Agaricise. Numerous instances, 

 the genera Echinopora, Merulina, for example, evince that the 

 mere fact of the polyp-mouths being confined to one surface or not is 

 comparatively unimportant, as the same species sometimes exemplifies 

 in its different parts the two modes of growth. The glomerate species 

 form part of the group Siderastrsea, of Blainville. The Thamnas- 

 terise of Sauvage, may be in part here included. 



The name of the genus alludes to the gracefully spreading forms 

 often presented by the species, and is from the Latin pavo, peacock. 



Arrangement of the Species. 



I. Unifacial; hypocrateriform. 



*1. P. explanulata. 



II. Unifacial ; foliaceous. 



2. P. crispa. 4. P. elephantotus. 



*3. P. papyracea. 



III. Bifacial ; folia crispate. 



5. P. cactus. *8. P. venusta. 



*6. P. prsetorta. *9. P. divaricata. 



*7. P. formosa. *10. P. boletiformis. 



IV. Bifacial; folia nearly flat and not crispate. 



*11. P. frondifera. *13. P. lata. 



*12. P. decussata. *14. P. crassa. 



V. Glomerate or subramose. 



15. P. siderea. *17. P. clavus. 



16. P. latistella. 



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